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Copigmentation of cyanidin 3-O-glucoside with phenolics: Thermodynamic data and thermal stability

Kanha, Nattapong, Surawang, Suthat, Pitchakarn, Pornsiri, Regenstein, Joe M., Laokuldilok, Thunnop
Food bioscience 2019 v.30 pp. 100419
anthocyanins, cyanidin, dopamine, ferulic acid, fruit juices, heat production, mulberries, pH, pasteurization, temperature, thermal stability
The intermolecular copigmentation of cyanidin-3-O-glucoside (C3G) with three colorless phenolic compounds and its thermal stability were investigated. The influence of the copigment (ferulic acid, dopamine, or (+)-catechin), the pigment-to-copigment molar ratio (1 : 1, 1 : 10, and 1 : 100), the pH value (pH 3–7), and the temperature (20, 30, 40, and 50 °C) on the copigmentation effect, stoichiometric ratio (n), the equilibrium constant (K), and thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were obtained. The strongest immediate copigmentation reactions were observed at pH 3 and 1 : 100 molar ratio, being significantly higher with (+)-catechin, followed by ferulic acid and then dopamine. The greatest hyperchromic shift was found in the complex of C3G/(+)-catechin, which was reasonable for its n and K values of 0.7 and 17.1, respectively. Moreover, the reactions were favored at low temperature. The thermodynamic data indicated that all these complexes were formed by spontaneous exothermic reactions. The C3G/(+)-catechin complex at the molar ratio 1 : 100 exhibited the greatest thermodynamic properties, with negative values of ΔG° (−6.92 kJ/mol), ΔH° (−38.7 kJ/mol), and ΔS° (−108.0 J/K/mol). The C3G/(+)-catechin complex exhibited a low Ea value (78 J/mol), indicating greater thermal stability against temperature change compared with those with the other phenolic pigments. In addition, copigmentation of anthocyanins in mulberry juice with (+)-catechin significantly reduced the loss of anthocyanins during pasteurization (80 °C for 15 min).